Can I buy liquor and perfumes at changi departure hall
and bring on flight to Melbourne?when I reach Melbourne
am I allow to buy in melbourne duty free shop at upon arrival and bring out?
Yes, and yes, but you need to keep the import limits in mind. Australia lets you bring in two litres of booze, and $800 worth of miscellaneous other stuff (which includes perfumes).
There's duty-free shopping airside when you arrive at Melbourne (before you clear customs), and when you leave as well (after you clear customs on the way out). They've got the good stuff, too - I've seen bottles of Grange and Mount Mary Quintet on the shelves at the duty-free store airside in Departures.
Pro tip - if you spend more than $300 in a single receipt in Australia, hang onto the receipt and you can claim back the 10% GST when you leave; look for the Tourist Refund Services booth just after you clear customs.